Jim,
Do you have the tool to remove the locking ring behind the steering wheel? Don't need it but you will cuss me until next week if you start and can't get that ring off!
Pull the wheel of along with the horn wiring-little tube with a single wire and a spring- take it out and put them some where safe. Unhook the main 9 wire (+/-) flat plug from the column. Then there is a 3 or 4 heavy wired plug with connectors on both ends, take this out and this will be the one you modify for the key switch.
OK, pull off the slotted ring from the column, it's circular with about 10 slots in it. (This is what locks your column when you pull the GM key out.
UNHOOK YOUR POSITIVE SIDE OF THE BATTERY-FIRST BEFORE ANYTHING!
Even before doing anything you need to order an ignition and key set-tumbler- and key bezel, all for a 65-66 etc. mustang. Almost every older Ford used this key and ignition set up. Make sure the spring comes with your ignition kit! (I buy the entire key set up from "California Mustang" They can be found on the net.)
Allright now you have the wires disconnected and the parts ordered-time for the body work. The housing that has the GM tumbler in it.... When you get the locking plate off look down inside where the key ignition comes through the column, you will see one screw that hold the entire tumbler in place. Remove the screw and now the GM ignition will come out in your hand.
Grind or cut off the part that sticks out for the GM key I use a small air saw to cut them off. Cut/sand/grind it all off flush with the main body of the column. Auto parts store: Purchase a 3M hard rubber repair kit- parts A & B---on the inside of the collar where the key was- you now should have a 1" +/- hole- using 2'" masking tape/duct tape cover the hole-following the contour of the cover/cap. Now mix up A&B and very carefully apply it to the outside of the column/sleeve carefully not to push in your taping.
Once that is dried and sanded with 80grit and put another light coat of body filler on top spreading it out past the A&B. Finish it off like a normal repair, prime with "plastic primer", wet sand when. When your satisfied with you work paint any color you desire- Usually flat black..
When that's all done let me know and I will tell you how to wire up your new switch. Normally there is enough wiring to put the new Ford key switch in the normal posistion-right side bottom of the column.
Clear as the Mississippi?
OR, pull the column, take off the wheel, remove the horn wire and send me the column with the short harness, parts and I'll build it for you.
DV